behzad maghsoudi department of anesthesiology, shiraz anesthesiology and critical care research center, shiraz university of medical sciences, shiraz, ir iran seyed hesamodin tabei department of anesthesiology, shiraz anesthesiology and critical care research center, shiraz university of medical sciences, shiraz, ir iran; department of anesthesiology, shiraz anesthesiology and critical care research center, shiraz university of medical sciences, shiraz, ir iran. tel: +98-7116474270, fax: +98-7116474270 farid zand department of anesthesiology, shiraz anesthesiology and critical care research center, shiraz university of medical sciences, shiraz, ir iran hamidreza tabatabaee department of epidemiology, school of health, shiraz university of medical sciences, shiraz, ir iran armin akbarzadeh student research committee, shiraz university of medical sciences, shiraz, ir iran